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MFA pH Controller

Most process plants generate a wastewater effluent that must be neutralized prior to discharge or reuse. Consequently, pH control is needed in just about every process plant, and yet a large percentage of pH loops perform poorly. Results are inferior product quality, environmental pollution, and material waste. With ever increasing pressure to improve plant efficiency and tighter regulations in environmental protection, effective and continuous pH control is highly desirable.

A strong-acid-strong-base pH process is highly nonlinear. The pH value versus the reagent flow has a Logarithmic relationship. Away from neutrality, the process gain is relatively small. Near neutrality where pH=7, the process gain can be a few thousand times higher. There is no way for a fixed controller like PID to effectively control this process. In practice, most pH loops are in a "bang-bang" type of control with pumps turning on and off resulting in large oscillations. Since acid and caustic neutralize each other, over-dosing acid and caustic is prohibitively expensive. Statistics show that a poorly controlled pH process can cost tens of thousands of dollars in chemical usage each month not counting the penalties imposed by violating EPA or local government discharge code.

The MFA pH controller can effectively control a wide range of pH processes within the full pH range. It is useful for wastewater neutralization and also enables automatic control of acid or alkaline concentration, both of which are critical quality variables for the chemical process industry.

MFA pH Controller Configuration

As shown in the following graph, one can easily enter Break Point A and B to define the estimated shape of the titration curve of the pH process. Then the MFA controller gain Kc for the flat portion and steep slope can be entered. For a strong-acid-strong-base pH process, if the controller gain for the flat portion is 1, then the gain for the steep slope can be estimated as 0.001, which is 1000 times smaller. Due to the adaptive capability of the MFA controller, the titration curve does not have to be accurate. In fact, its shape can vary in real applications. In addition, the flow rate and the pH value of the inflows may vary significantly. The MFA pH controller can effectively deal with these large disturbances.

MFA pH controller configuration menu

The MFA pH controller has helped many users effectively control their tough pH loops. Payback in weeks or even days has been reported with savings on chemical reagents, avoiding violation of discharge codes, and smoother production operations.

View controller video  .9 MB ( Macromedia Shockwave plug-in required )



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